> Here's my thoughts. First, an amplifier with output
> devices (note-
> tubes or solid state) will have a certain absolute maximum
> output
> power capability. There is a point at which the tube(s)
> cannot produce
> additional RF. If an attempt to exceed that level is made
> it
> merely flat-tops and creates trash in addition to the
> desired signal.
That "trash" starts at anything over zero watts Ed, and it
can get better and worse as power is increased. Transistors
of course limit with a much more defined change in transfer
characteristics than tubes, and the angle of the slope
actually controls the distortion....not the fact the
transfer characteristic diverges from a straight line.
> That can be measured easily watching a 'scope and looking
> for the peaks.
> You could just key down and go for maximum smoke.
> Either method could be used to measure the output
> capability of an
> amplifier.
It would not.
Flat-topping on a scope tells us very little about bandwidth
or adjacent channel trash. It's like using a rubber ruler.
> However, to assume that PEP is 2 x key down is misleading.
> The
> unit may not be capable of the 2 x level, see above. I
> guess this value
> was derived when we started measuring output as opposed to
> DC input
> with the advent of SSB.
I'm constantly amazed by the the number of amateurs who are
supposed to (by law) run a certain maximum power level, but
who do not know what the measurement terms mean. One would
think it would be a go/ no-go part of the test to run the
equipment, like reading a speedometer in a car.
> It is misleading to assume that voice is symetrical, and
> peaks are
> only 2x CW level.
The two are entirely unrelated and unimportant as is
waveform symmetry in a SSB transmitter. This is not AM where
we are not allowed to reach or exceed zero carrier on
negative peaks. It is SSB, and "at or below zero" is just
fine.
>Having worked in broadcasting most of my life I can
> attest to this. Look at some of the processing devices.
> SymmetriPeak,
> early on device with a set of saturated coils hoping to
> balance + & - levels of voice. Later it was noted FCC
> Rules had no max
> for positive modulation. So we now "phased" mikes so all
> positive peaks were
> in the same direction, only limiting negative peaks.
AM and SSB are not the same.
> On and on the story goes. But for me amplifiers should be
> rated at there key
> down
What if we only have a microphone, or use a swicth instead
of a key?
What if HV changes? What about ALC?
> maximum, period. SSB can only be less total power, which
> results in good
> sounding signals (no clipping).
That's not factual. SSB peaks can be and often are
significantly higher than steady carrier conditions, and
they can do that without undue distortion.
If you want to know IMD or occupied bandwidth, you need to
actually measure it in the working system with voice or
something that **very closely** approximates voice. If you
want to measure peak envelope power, and it is a nearly
perfect measurement method, you need a simple peak storage
meter.
I can't measure IM on a time domain voltage display
(o-scope) just like I can't measure the frequency of a sharp
transient on a spectrum analyzer sweeping at a few
milliseconds or seconds per sweep, or predict system
impedance or Q or instability frequency with a GDO.
There's nothing worse than an absolute measurement based on
the wrong instrument or measurement method. Better to not do
it at all than to come up with an absolute cast-in-stone
answer that is really just an uncontrolled random guess.
73 Tom
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